Microwaves are understood to be electromagnetic radiation in a frequency range of approximately 300 MHz to 300 GHz generated with the help of microwave generators. Microwaves are sent from a microwave generator through a hollow conductor or coaxial cable to their site of use where they are output via an antenna, for example, which projects by at least one quarter of the wavelength into a shielded chamber. In this chamber, the microwaves interact with the parts to be heated.
For heating parts by means of microwaves, in principle two different devices are differentiated:
With one device, the microwaves are radiated into a chamber whose dimensions are much larger than the wavelength. The microwaves are reflected on the walls of the chamber and are superimposed to form a complex field distribution (multimode). However, microwaves cannot be concentrated spatially in such a chamber, so defined heating of certain sections of a part is not possible. The chamber has the function of determining the field distribution and protecting the operator of the device from microwaves.
With the other device, the microwaves are radiated into a chamber whose dimensions correspond approximately to the wavelength, so that a defined field distribution (monomode) develops within the chamber. However, with such a chamber, defined spatial heating of parts can be achieved only to a limited extent, because this field distribution is not homogeneous in space. Thus, the chamber here has the function of defining the field distribution and again protecting the operator from microwaves.
With these devices from the related art, the parts can thus be heated only as a whole or in nonhomogeneous sections, although that is neither desirable nor necessary for most applications. Furthermore, implementation of an opening necessary for introduction of the parts into the shielded chamber is complicated with these devices, because such openings in that location are feasible only by means of doors or microwave absorbers.